Production of high purity cyclohexane concentrate



Aug. 5, 1958 G. H. MEASON ET-AL PRODUCTION OF HIGH PURITY CYCLOHEXANECONCENTRATE Filed June 16, 1955 I3 ssm/ur/ow 20/15 I armor/5x4! H PLANTFEED A sroc/r fiAFF/NATE EXTRACT/V5 DISTILLAT/O/V ZONE EXTRACT FRA6TIONszao/va /8- DIST/LL A no ISOHER/ZA now] INVENTORS. George H. Manson,

Y Thomas M. Newsam,

A r TOR/V5 Y.

Ulliifid PRODUCTISN 6F HIGH PURXTY CYCLOHEXANE C(BNCENTRATE ApplicationJune 16, 1955, Serial No. 515,952

2 Claims. (Cl. 260-666) The present invention is directed to a procedurefor preparing a pure hydrocarbon. More particularly the presentinvention is directed to a process for preparing a high puritycyclohexane concentrate from a feed stock consisting of a close boilingmixture of saturated and aromatic hydrocarbons having 6 and 7 carbonatoms in the molecule and isomers of cyclohexane including n-hexane,benzene, methylcyclopentane, cyclohexane, and dimethylpentanes. Theprocess of the present invention is applicable to a hydrocarbon feedstock which contains at least by volume of benzene and in which theratio of cyclohexane to benzene is no greater than 3 to 1 by volume. Theprocess of the present invention is particularly useful when the benzenecontent of the cyclohexane product must be reduced to less than 0.5%. Inaccordance with the present invention, a high purity cyclohexaneconcentrate containing at least 95% by volume cyclohexane and up togreater than 99.5% purity cyclohexane may be secured.

Further objects and advantages of the present invention may be seen fromthe following description taken in conjunction with the drawing in whichthe sole figure is in the form of a diagrammatic flow sheet.

In certain commercial operations, as in a petroleum refinery, a mixtureof close boiling hydrocarbons is available. For convenience, thisfraction may be referred to as cyclohexane plant feed stock. This feedstock may contain n-hexane, benzene, methylcyclopentane, cyclohexane anddimethylpentanes and other hydrocarbon. The boiling points of thesecompounds are set out in Table I By way of example in Table II hereafteris given the composition of a typical plant cyclohexane feed stock:

tes atent 2,846,485 Patented Aug. 5, 1958 ice High purity fractions,particularly cyclohexane in the range given, may be secured from such amixture of hydrocarbons.

It is to be understood that this typical composition is given by way ofexample only and that actually cyclohexane feeds containing varyingamounts of benzene may be satisfactorily treated in accordance with thepresent invention provided the benzene content is above 5%. For example,feed stocks containing from about 5% to about 30% benzene may beemployed. The benzene and cyclohexane contents may vary as shown inTable III:

Table III Benzene, percent vol.: Cyclohexane, percent vol. 20 Up to 6010 Up to 30 5 Up to 15 Turning now specifically to the drawing, a feedstock which may suitably consist of n-hexane, benzene,methylcyclopentane, cyclohexane and dimethylpentanes, designated in thedrawing as cyclohexane plant feed stock, is passed through inlet line 11to separation zone A where it is separated into a first fraction whichis a benzene concentrate and removed through outlet line 12 and a secondfraction containing the remaining portions of the feed stock and removedthrough outlet line 13. The separation carried out in separation zone Amay be secured by the use of any one of several well known procedures.By way of specific example, the separation may be carried out byextractive distillation or solvent extraction or absorption. The use ofthese procedures is well known to the art. It will often be foundpreferable.to employ extractive distillation for carrying out theseparation in zone A and a process of such character for the separationof aromatic hydrocarbons is described in U. S. Patent 2,288,126. Ifextractive distillation is used to conduct the separation in zone A thebenzene fraction removed through line 12 may be considered the extractfraction and the fraction removed through line 13 may be considered therafiinate fraction.

The fraction passing through line 13 has admixed therewith from line 14another fraction consisting of a mixture of methylcyclopentane,cyclohexane, and traces of heavier material. The origin of this fractionwill be described hereafter. The resulting admixture passes into thefirst fractional distillation zone B where it is separated into abottoms fraction removed through line 15 and an overhead fractionremoved through line 18. The bottoms fraction in line 15 may containfrom about to about by volume of cyclohexane. The bottom fraction inline 15 then passes to an extractive distillation zone C where it isseparated into a raifinate fraction removed from the system throughoutlet line 16 and an extract zone B removed through line 18 consists ofa mixture of' n-hexane, dimethylpentanes and methylcyclopentane, and atrace of lower boiling components and is chargedto isomerization zone Dwhere at least a substantial portion of the methylcyclopentane contentis converted to cyclohexane. The isomerization of methylcyclopentane tocyclohexane is known to the art. This isomerization step mayconveniently be carried out as a catalytic process using for example aFriedel-Cra-fts type of catalyst such as promoted aluminumchloride, suchas with HC1 and the like. the range of 120 F. to 250 F. with a spacevelocity of .2 to 2.'v.'/v./hr. The effluent from isomerization zone Dpasses through line 19 to second fractional distillation zone B where itis separated into an overhead fraction consisting principally ofn-hexane and lighter materials which may be formed in the isomerizationzone and which is withdrawn through line 20 and discarded from thesystem and. a bottoms fraction consisting of methylcyclopentane,cyclohexane and traces of heavier material which may be formed in'theisomerization .zone and which is withdrawn through line 14 and admixedwiththe fraction in line 13 as previously described.

As an alternative procedure, in addition to the bottoms passed fromdistillation zone B to extractive distillation zone C for separationtherefrom of high purity cyclohexane, a fraction from an extraneoussource containing within the range of 65% to 95% cyclohexane andexcluding as far. as possible methylcyclopentanes and compounds boilinglower than methylcyclopentane and no more than 'of fractionshigher'boiling than cyclohexane may be introduced through line 21-andadmixed with the fraction in line 15, the mixture passing to extractivedistillation unit 0 for separation of a raflinate fraction withdrawnthrough line 16*and an extract fraction withdrawn "through line 17 andcontaining-cyclohexane of at least 95% purity.

-From'the foregoing description, it will be evident that the process ofthe present invention allows the processing of a mixture of closelyboiling hydrocarbons in such a manner as to recover efiiciently maximumamounts of high purity cyclohexane concentrates therefrom. In addition,other desirable materials such as benzene and n-hexane fractions arealso recovered in the process of the present invention.

Operating temperatures are preferably within The invention claimed is: p

l. A process for the preparation of high purity cyclohexane and highpurity benzene and for the maximum recovery of both cyclohexane andbenzene from a feed stock comprising n-hexane, benzene,methylcyclopentane, cyclohexane and dimethylpentanes which comprises thesteps of passing the feed stock to a first extractive distillation zoneand there separating the feed stock into an extract fraction containingsubstantially the whole of the benzene in the feed stock and intoaraflinate fraction substantially free of benzene and containing theremainder of the feed components and removing said extract fraction as afirst fraction from the system, admixing said ralfinate tainingmethylcyclopentane, passing the fifth fraction to an isomerization zoneand there converting at least a substantial portion of itsmethylcyclopentane content into cyclohexane, passing theefiluent fromsaid isomerization zone into a second fractional distillation zone andthere. separating it into :an overhead fraction and a bottoms: fraction,removing said overhead fraction as a sixth fraction containing n-hexaneand lighter materials from the system, taking the bottoms fraction assaid third fraction containing methylcyclopentane, cyclohexane andheavier material and admixing it with said second fraction as previouslydescribed and charging the fourth "fraction as feed .to a secondextractive distillation zone and therein separating 3a rafiinatefraction containing dimethylpentane and other parafiinic materials andan extractfraction containing high purity cyclohexane and separatelyremoving said :last rafiinate and said last extract fraction from saidsecond extractive distillation zone.

2. A process as described in claim 1' wherein the feed stock contains atleast 5% by volume of benzene; the

feed stock has a ratio of cyclohexane to benzene no greater than 3 to 1by volume; the fourth fraction contains 8010 cyclohexane; and theextract fraction from the second extractive distillation zone containsat least 95% cyclohexane.

References Cited inthe file of this patent UNITED STATES PATENTS I2,475,828 Far kas et a1. July 12, .1949 2,493,567 Birch et a1. Jana,195.0 2,540,318 Birchret a1 "Feb. 6, 1951

1. A PROCESS FOR THE PREPARATION OF HIGH PURITY CYCLOHEXANE AND HIGH PURITY BENZENE AND FOR THE MAXIMUM RECOVERY OF BOTH CYCLOHEXANE AND BENZENE FROM A FEED STOCK COMPRISING N-HEXANE, BENZENE, METHYLCYCLOPENTANE, CYCLOHEXANE AND DIMETHYLPENTANES WHICH COMPRISES THE STEPS OF PASSING THE FEED STOCK TO A FIRST EXTRACTIVE DISTILLATION ZONE AND THERE SEPARATING THE FEED STOCK INTO AN EXTRACT FRACTION CONTAINING SUBSTANTIALLY THE WHOLE OF THE BENZENE IN THE FEED STOCK AND INTO A RAFFINATE FRACTION SUBSTANTIALLY FREE OF BENZENE AND CONTAINING THE REMAINDER OF THE FEED COMPONENTS AND REMOVING SAID EXTRACT FRACTION AS A FIRST FRACTION FROM THE SYSTEM, ADMIXING SAID RAFFINATE FRACTION AS A SECOND FRACTION WITH A THIRD FRACTION CONTAINING METHYLCYCLOPENTANE, CYCLOHEXANE, AND HEAVIER MATERIAL, DISTILLING THE ADMIXED SECOND AND THIRD FRACTIONS IN TOMS FRACTION AND AN OVERHEAD FRACTION, REMOVING THE BOTTOMS FRACTION AS A FOURTH FRACTION CONTAINING CYCLOHEXANE, REMOVING THE OVERHEAD AS A FIFTH FRACTION CONTAINING METHYLCYCLOPENTANE, PASSING THE FIFTH FRACTION TO AN ISOMERIZATION ZONE AND THERE CONVERTING AT LEAST A SUBSTANTIAL PORTION OF ITS METHYLCYCLOPENTANE CONTENT INTO CYCLOHEXANE, PASSING THE EFFLUENT FROM SAID ISOMERIZATION ZONE INTO A SECOND FRACTIONAL DISTILLATION ZONE AND THERE SEPARATING IT INTO AN OVERHEAD FRACTION AND A BOTTOMS FRACTION, REMOVING SAID OVERHEAD FRACTION AS A SIXTH FRACTION CONTAINING N-HEXANE AND LIGHTER MATERIALS FROM THE SYSTEM, TAKING THE BOTTOMS FRACTION AS SAID THIRD FRACTION CONTAINING METHYLCYCLOPENTANE, CYCLOHEXANE AND HEAVIER MATERIAL AND ADMIXIN G IT WITH SAID SECOND FRACTION AS PREVIOUSLY DESCRIBED AND CHARGING THE FOURTH FRACTION AS FEED TO A SECOND EXTRACTIVE DISTILLATION ZONE AND THEREIN SEPARATING A RAFFINATE FRACTION CONTAINING DIMETHYLPENATE AND OTHER PARAFFINIC MATERIALS AND AN EXTRACT FRACTION CONTAINING HIGH PURITY CYCLOHEXNE AND SEPARATELY REMOVING SAID LAST RAFFINATE AND SAID LAST EXTRACT FRACTION FROM SAID SECOND EXTRACTIVE DISTILLATION ZONE. 